Corrosion-inhibited phosphate solutions and compositions useful for manufacturing them



directed toward this particular end use.

should be kept in mind that the invention is generally- United 3 257,316 CORROSION-INHIBHTED PHOSPHATE SOLUTIONS AND COMPOSITIONS USEFUL FOR MANUFAC- TURING THEM Robert P. Langguth, St. Louis, and William W. Morgenthaler, Bridgeton, Mo., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Feb. 23, 1965, Ser. No. 434,630 11 Claims. (Cl. 252-4) This application is a continuation-in-part of United States application Serial No. 235,866, filed November 6, 19.62, and now abandoned.

This invention relates to improved aqueous solutions of phosphate salts, which solutions are characterized by having as significantly reduced tendency to corrode copper metal and copper-containing alloys. More specifically, the present invention relates to corrosion-inhibited ammonium phosphate solutions suitable for prolonged use in handling and storage equipment made of copper and/ or copper alloys.

Aqueous ammonium phosphate solutions have many uses: One of the most valuable recent developments in the field of fire fighting, and more particularly, forest fire fighting, was that relating to the use of aqueous solutions of ammonium phosphate salts. Since the present invention is particularly valuable when practiced in connection With forest fire fighting, the present discussion will be However, it

useful for inhibiting corrosion of copper by ammonium phosphate solutions. Ordinarily, the solutions (often thickened with a viscosity modifying agent so that the solutions stick readily to surfaces with which they come into contact) are dropped onto brush, trees and dry grass in the path of a fire in order to slow or stop the progress of the fire. The extensive use of such ammonium phosphate solutions for forest fire control has been slowed because of the concern by those in the field over the natural corrosivity of such aqueous ammonium phosphate solutions toward some of the vital parts of air-tankers and storage equipment.

While, ordinarily, aqueous solutions containing several weight percent of dissolved ammonium phosphate are not considered to be extremely corrosive toward copper metal or copper alloys such as brass and bronze and the like, they are, nevertheless, sufficiently corrosive to cause great concern when the aqueous solutions are to come into physical contact with vital aircraft parts, since failure of the aircraft parts due even to slow corrosion occurring over a prolonged period of time could result in the loss of the aircraft and crew. Thus, in order to .be considered completely acceptable for use in forest fire fighting by the air-drop method, it is necessary that the corrosivity of aqueous ammonium phosphate solutions, particularly toward copper metals, be significantly reduced.

Consequently, it is an object of the present invention to provide aqueous solutions containing ammonium phosphate salts useful for forest fire fighting, the normal tendency of which to corrode copper and copper-con taining alloys is significantly reduced or substantially eliminated.

It is another object of the present invention to provide novel methods of inhibiting the corrosion of copper equipment by aqueous ammonium phosphate solutions.

It has now been found that the normal or natural tendency of aqueous solutions of ammonium phosphate salts, such as, for example, monoammonium orthophosphate and diammonium orthophosphate to corrode copper equipment can be significantly reduced and even practically eliminated by the presence (in solution) of an effective effected by such a reaction.

' 3,257,316 Patented June 21, 1966 ganic cyanide compounds that are soluble at ambient temperatures in the aqueous ammonium phosphate solutions to be inhibited to at least the extent at which they can discernably reduce copper corrosion (i.e., generally at least about 0.005 weight percent). For example, this term includes such complex cyanide compounds as the alkali metal and ammonium ferrocyanides, ferricyanides and nitroprussides. Of these, the sodium, ammonium and potassium ferrocyanides, ferricyanides and nitroprussides are generally preferred, although, for economic reasons, the sodium and ammonium ferrocyanide and ferricyanide salts are particularly preferred.

The term water-soluble complex. cyanide also includes alkaline earth metal ferr'ocyanides, ferricyanides, and nitroprussides (such as calcium ferrocyanide, calcium ferricyanide, and calcium nitroprusside and the corresponding magnesium, rubidium, cesium, and franciurn salts) and other similar materials that simply meet the above-described solubility test, including for example but not limited to, thallium ferrocyanide, ferro'cyanic acid, ferricyanic acid, silver ferricyanide, sodium nitroferricyanide, ammonium nitroferrocyanide, barium nitroprusside, barium ferricyanide, strontium ferricyanide, sodium hydroxy ferricyanide, potassium hydroxy ferricyanide, sodium ammonia 'ferricyanide, fran'eium nitroprusside, and the like.

This wide variety of material canbe used as the source of the corrosion inhibiting anion (complex cyanide anion) in the practice of this invention because, apparently, it is the complex cyanide anion that is performing the desired corrosion inhibition of copper. particular cation attached to the complex cyanide anions useful in the practice of the invention is apparently unimportant. What is important is that enough of the complex cyanide anions find their way into the ammonium phosphite fire-fighting solutions (described hereinafter in detail) to achieve the desired copper corrosion inhibition. Apparently the only controlling element, then, in this respect, is the actual solubility of the compound in the ammonium phosphate solutions. The fact that some of the heavy metal and alkaline earth metal cations of the complex cyanide materials specified above might react with some of the phosphate in these solutions is not a problem because, nevertheless, the effective anion remains in solution to perform its corrosion inhibiting function and at most, only a small proportion of the phosphate can be involved in such a reaction with these heavier cations. Neither would the fire retardency properties of the solutions of the present invention be substantially The ammonium phosphate solutions in which these complex inorganic cyanide compounds perform particularly effectively .are those that contain at least about 0.5 weight percent, and up to the level at about which the solutions are saturated therewith,- but preferably between about 5 and about 25 weight percent of dissolved ammonium phosphate salts, including monoammonium orthophosphate and/or diammonium orthophosphate salts, and also including the diammonium and monoammonium mixed orthophosphate salts that also contain an alkali metal cation, such as monoammonium disodium orthophosphate, monoammonium dipotassium orthophosphates and the like, no matter from what source these materials were derived, or in what form the materials are initially introduced into the aqueous compositions. Generally, it is preferred that the inhibited aqueous phosphate solutions of this invention have a pH between about 3 and about 9. Then monoammonium orthophosphate is Thus, the

the only ammonium phosphate salt present in the inhibited fire-control compositions of this invention, the preferred pH of these compositions is generally from about 3 to about 5. Similarly, when diammonium orthophosphate is the only ammonium phosphate salt contained therein, the preferred pH is from about 7 to 9. When mixtures of monoammonium orthophosphate and diammonium orthophosphate are utilized, pHs between these preferred ranges are generally more desirable. However, compositions having pHs somewhat higher or lower than these preferred ranges can also be utilized to advantage in the practice of the present invention.

Although the presence of even a very small amount of the water-soluble complex inorganic cyanide compounds in the aqueous ammonium phosphate solutions described above has a corrosion-inhibiting effect upon them, as a general rule aqueous phosphate compositions containing at least about 0.01 and preferably at least about 0.04 of one or more of the complex inorganic cyanide compounds in the dissolved state should be utilized. Generally optimum corrosion-inhibiting effects can be attained by utilizing at least about 0.10 weight percent of the complex inorganic cyanide compound. Actually, the particular source (or compound) from which the complex cyanide anions are derived in the manufacture of the aqueous ammonium phosphate solutions is apparently not critical, provided a suflicient amount of these anions are provided in the dissolved state to effectively decrease the normal corrosivity of the phosphate solutions toward copper and copper-containings alloys. Thus, the final fire-control compositions of this invention should generally contain from about 0.008 to about 8, and preferably from about 0.03 to about 1.6 weight percent of the complex cyanide anions dissolved therein.

The corrosion-inhibited ammonium phosphate solutions of the present invention can also contain materials other than the phosphate salts and the complex inorganic cyanide compounds without detracting substantially from the benefits that can be obtained by practicing this invention. For example, the solution can contain minor amounts of surfactants; inorganic and organic complexing agents such as the alkali metal tripolyphosphate, pyrophosphates and trimetaphosphates, as well as the higher polyphosphates such as the hexametaphosphates and also can contain ethylenediamine tetra-acetic acid and various alkali metal and ammonium salts thereof, and the alkali metal and ammonium nitrilotriacelates; any of the various thickening agents such as carboxymethylcellulose, algin, guar gum and carboxyethylcellulose; other cor rosion-inhibiting ingredients; and inorganic and organic pigments and dyes; as well as many other materials.

The corrosion-inhibited phosphate compositions of this invention can be manufactured via any of a number of methods without any noticeably determined effects upon the ultimate performance of the compositions. For example, the complex cyanide compound can simply be dissolved by intermixing it into or with the otherwise completely formulated aqueous compositions, or at any other stage during the preparation of the fire-control composition. Via another method the complex cyanide compound can first be dissolved in water, and the resulting solution then intermixed subsequently with the ammonium phosphate materials.

Still another process for manufacturing the aqueous corrosion inhibited phosphate compositions described heretofore involves one of the preferred embodiments of the present invention. This preferred embodiment comprises making a concentrate mixture of one or more of the ammonium phosphate salts described heretofore with one or more of the complex cyanide (inhibitor) compounds, generally in a particulated, solid form.

Preferably the inhibitor compound(s) and ammonium.

phosphate salt(s) will be preesnt in this concentrate composition or mixture in amounts proportionate to those found in the fire-control compositions described heretofore,

so that the final fire-control composition can be manufactured by simply dissolving the concentrate in a sufficient amount of water. In other words, generally, the preferred concentrate compositions of this invention will contain at least one of the above-described ammonium phosphate salts and at least one of the complex cyanide (inhibitor) compounds in a weight ratio of phosphate salts to inhibitor compound, respectively, of from about 380021 to about 15:1 and preferably from about 760:1 to about 100:1. It is still further preferred that these particulated, solid concentrate compositions contain a total of at least about 50 Weight percent of one or more of the above-described ammonium orthophosphate salts. These preferred concentrate compositions can also contain effective amounts of practically any other ingredients including a thickener if one is desired in the final firecontrol compositions, as well as dyes, pigments, watersoftening agents, and the like, all of which should preferably be present in the concentrate compositions in minor amounts, as compared to the ammonium phosphate salt(s) contained therein. Some of the advantatages of these preferred concentrate compositions can readily be appreciated when it is realized that at most points from which aircraft are loaded for their various air-drops of fire-control compositions, very little weighing and handling equipment is available that is capable of manufacturing the fire-control compositions from the individual components. Thus, in the absence of the preferred concentrate compositions described above (which concentrate composiitons need simply be dissolved in appropriate amounts of water in order to be converted into the final, valuable fire-control compositions of the present invention), as a practical matter, such corrosion inhibited final fire-control compositions as those described heretofore could not be utilized.

Typical examples of the preferred concentrate compositions of this invention include:

(a) 99.0 weight percent of diammonium orthophosphate and 1.0 weight percent of sodium ferricyanide.

(b) 90.0 weight percent of monoammonium orthophosphate, 1.0 weight percent of sodium ferrocyanide and 9.0 Weight percent of sodium alginate.

c) weight percent of diammonium orthophosphate, 0.5 weight percent of sodium ferrocyanide and 9.5 weight percent of carboxymethylcellulose.

(d) 88 weight percent of diammonium orthophosphate, 0.50 weight percent of sodium ferricyanide and 11.5 weight percent of algin.

(c) 84.0 weight percent of diammonium orthophos: phate, 0.25 weight percent of potassium ferrocyanide and 15.75 weight percent of guar gum.

(f) 99.60 weight percent of monoammonium orthophosphate, 0.40 Weight percent of sodium ferricyanide.

(g) 89.75 weight percent of monoammonium orthophosphate, 0.25 weight percent of sodium ferrocyanide and 10.00 weight percent of algin.

(h) 85.0 weight percent of monoammonium orthophosphate, 0.25 weight percent of potassium ferrocyanide and 14.75 weight percent of guar gum.

(i) 99.8 Weight percent of diammonium orthophosphate and 0.20 weight percent of sodium ferrocyanide.

(j) 88.00 Weight percent of diammonium orthophosphate, 0.30 weight percent of sodium nitroprusside and 11.70 weight percent of carboxymethylcellulose.

(k) 89.00 weight percent of diammonium orthophosphate, 0.40 weight percent of sodium nitroprusside and 10.60 weight percent of algin.

(l) 86.00 weight percent of diammonium orthophosphate, 0.50 Weight percent of potassium nitroprusside and 13.50 weight percent guar gum.

(m) 99.75 Weight percent of diammonium orthophosphate and 0.25 weight percent of sodium nitroprusside.

(11) 99.50 weight percent of monoammonium orthophosphate and 0.50 weight percent of sodium nitroprus; side.

(0) 89.00 weight percent of monoammoniurri orthophosphate, 0.20 weight percent of potassium nitroprusside and 10.80 weight percent of algin.

These concentrate compositions are also useful as corrosion-inhibited de-icer compounds, wherein either alone or in combination with additional corrosion inhibiting materials, they can be utilized in a manner similar to that in which more corrosive, less desirable, sodium chloride is presently conventionally utilized. For example, these particulated, solid ammonium phosphatecomplex cyanide compounds can effectively de-ice sidewalks, roadways and the like when they are simply spread over ice and/or snow.

The concentrate compositions can be prepared via any of a number of convenient procedures, including simply blending or mixing together the appropriate amounts of the various dry ingredients. They can also be prepared by first dissolving the respective ingredients in water and subsequently drying the resulting solution in a convenient manner such as on a steam-heated drum-drier, or by use of conventional spray-drying equipment. Although the size of the individual particles in these preferred concentrate compositions is not critical in so far as the practice of the present invention is concerned, it is generally preferred that they be of sufficiently small size to pass through a U8. standard 12 mesh screen. For optimum results, at least about 80 weight percent of these particles should be small enough to pass through a US. standard 40 mesh screen. Although commercial grades of phosphate salts do not necessarily meet these optimum standards of particle size, they can readily be utilized in the preparation of the compositions of this invention.

In the following examples which are illustrative of some of the preferred embodiments of the present invention, all parts given are by weight unless otherwise specified.

6 anide. The resulting mixture is then stirred until all of the diammonium o-rthophosphate has dissolved.

' Into the resulting fire-control composition are immersed several clean,- preweighed soft copper (1 x 2" x A coupons. The coupons are continuously immersed and removed from the composition in a cycle adjusted so that the coupons remain immersed in the composition for 30 seconds, and then remain out of the solution, exposed to the ambient air, for 30 seconds. This procedure is continued for a total of 72 hours, after which the coupons are removed from the fire-control composition, rinsed with distilled Water and acetone and then reweighed. The loss in weight (in milligrams) is then appropriately inserted into the equation:

orrosion in mi s per year.

wherein;

W=weight lost during test in miligrams, D=speci-fic gravity of metal,

A=exposed surface area in square inches, T=time of exposure to solution in hours,

sodium ferrocyan-ide, corr-odes similar copper coupons ata rate of about 1,000 mils per year.

In a manner similar to that just described other compositions containing various levels of inorganic complex cyanide compounds are tested. Results of such tests are given in Table I, below:

TABLE 1.CORROSION INHIBTED AMMONIUM PHOSPHATE SOLUTIONS Example Ammonium Phosphate Parts Thiekener l Inhibitor Parts Metal gi No. (mp-v) 1, 500 7. 3 1, 300 940 1. 4 0. 5 0. 5 0. 5 do 0.3 10 Potassium Ferrieyanide 0. 6 10 OM0 Ammonium Ferrieyanide 0. 5 10 CMCL Sodium Nitroprusside 0.8 10 OM0 Potassium Nitroprusside 0.7 10 CMC Sodium Ferrieyanide 0.6 XII, {Diamrnomum Orthophosphateu CMCL d0 1. 5 Monoarmnonium Orthophosphate Diammonium Orthophosphate XIII Monoammonium Orthophosphate. .do 1. 5

Tetrasodium Pyrophosphate. IV Diammonium Orthoph0sphate. Sodium Ferroeyanide 1. 4 V 1 Calcium Ferrocyanide. 1. 9 Calcium Nitroprusside 2.0 Magnesium Ferrieyanide 0.5 Ammonium Nitroferroeyan1de 0.6 Ferroeyanic acid 1. 9 Barium Nitroprusside. 2. 5 Strontium Ferrieyanide. 2.6 Silver Ferricyanide 0.6 Sodium Hydroxy Ferricyamde 1. 7 Francium Nitroprusside. 0. 5

Monoammonium Orthophosphate 1 Rubldlum Ferrocyamde 0 Diammoniurn Orthophosphate 10 Monoammonium 0rthophosphate. 1 CMC Ferricyanic acid 0.05 Bronze 2. 7 Tetrasodium Pyrophosphate 3 XXVII Diammonium Orthophosphate 5 None Ammonium Ferroeyamde 0.05 Copper 0. 5

l Thiekener used at the 1 weight percent level, based on total weight of the composition.

2 Carboxymethyleellulose. I Example I Into a conventional steel storage tank fitted with a fairly eflicient mixer are charged 8.34 parts of water and 1.2 parts of a pre-prepared blend made up of 84 parts of crystalline technical grade diammonium orthophosphate, 15

parts of sodium alginate and l part of sodium ferrocysion ordinarily caused by aqueous solutions of ammonium orthophosphate, said composition consisting essentially of at least one ammonium orthophosphate salt selected from the group consisting of monoammonium orthophosphate and diammonium orthophosphate and a water-soluble inorganic complex cyanide compound; the weight ratio of said ammonium orthophosphate salt to said complex cyanide compound in said composition being from about 380011 to about :1.

2. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate, said composition consisting essentially of at least about 50 weight percent of an ammonium orthophosphate material selected from the group consisting of monoammonium orthophosphate, diammonium orthophosphate and mixtures thereof, and a complex cyanide compound selected from the group consisting of ammonium and alkali metal ferrocyanides, ammonium and alkali metal ferricyanides and ammonium and alkali metal nitroprussides; the weight ratio of said ammonium orthophosphate salt to said complex cyanide compound in said concentrate composition being from about 760:1 to about 15:1.

3. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is sodium ferrocyanide.

4. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is ammonium ferricyanide.

5. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is sodium nitroprusside.

6. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is ammonium ferrocyanide.

7. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is sodium ferricyanide.

8. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is ammonium nitroprusside.

9. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is potassium nitroprusside. a

10. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is potassium ferricyanide.

11. A particulated solid concentrate composition useful when dissolved in water to protect copper and copper alloys from corrosion ordinarily caused by aqueous solutions of ammonium orthophosphate as in claim 2, wherein said complex cyanide compound is potassium ferrocyanide.

References Cited by the Examiner UNITED STATES PATENTS Re. 23,740 11/ 3 Ryznar et a1 252-3 89 XR 2,303,399 12/1942 Schwartz 252389 XR 3,024,100 3/1962 Langguth et al. 252388 XR 3,127,932 4/1964 Schremp et a1 1661 3,182,018 5/1965 Chittum 252-387 XR FOREIGN PATENTS 225,481 11/ 1959 Australia. 575,798 5/1959 Canada.

JULIUS GREENWALD, Primary Examiner.

M. WEINBLATT, Assistant Examiner. 

1. A CONCENTRATED AMMONIUM ORTHOPHOSPHATE COMPOSITION SUITABLE FOR USE IN THE MANUFACTURING OF AQUEOUS CORROSION-INHIBITED AMMONIUM ORTHOPHOSPHATE FIRE-FIGHTING SOLUTIONS TO PROTECT COPPER AND COPPER ALLOYS FROM CORRSION ORDINARILY CAUSED BY AQUEOUS SOLUTIONS OF AMMONIUM ORTHOPHOSPHATE, SAID COMPOSITION CONSISTING ESSENTIALLY OF AT LEAST ONE AMMONIUM ORTHOPHOSPHATE SALT SELECTED FROM THE GROUP CONSISTING OF MONOAMMONIUM ORTHOPHOSPHATE AND DIAMMONIUM ORTHOPHOSPHATE AND A WATER-SOLUBLE INORGANIC COMPLEX CYANIDE COMPOUND; THE WEIGHT RATIO OF SAID AMMONIUM ORTHOPHOSPHATE SALT TO SAID COMPLEX CYANIDE COMPOUND IN SAID COMPOSITION BEING FROM ABOUT 3800:1 TO ABOUT 15:1. 